Hazard Resistant
Features of Walls and
Openings
National Disaster
Management Authority People in Centre
No. of Slides: 58Time: 45 min
C10
Gujarat Institute of
Disaster Management
1. Participants are aware of various damages inflicted upon
load bearing and in-fill walls during different hazards.
2. They know construction methods of mitigating impact of
hazards on walls (principles and design limits).
3. They are aware of safety features and measures for
increasing resilience of walls during hazards through
construction details (masonry bonds, corner junctions, vertical
reinforcements etc.).
Expected Outcomes
2
1. Infill Walls: When the load of the roof is transferred to the
ground by columns and beams, the walls take only their self-
weight. Such walls are known as infill walls.
3
Wattle and daub
Types of Walls
Brick Infill Wall
2. Load Bearing Walls: Walls which transfer the load of the roof
or floor above to the ground are known as Load Bearing Walls.
4
Adobe bricks Rammed Earth Fired bricks
Load Bearing Walls: Load bearing walls with different materials
5
Hollow
Concrete
Blocks
Uncoursed
Random
Rubble
Stone
Random
Rubble
Stone
Ashlar
Stone
3. Confined Masonry Walls: The load is taken by the masonry
walls as well as the RC elements. Further, the RC elements
confine the units at corners and junctions, strengthening the
structure against lateral forces.
6
The RC corners as well as the brick masonry is constructed
together and integrated well with each other.
7
Difference between Confined Masonry and RC
Frames with Infill Walls
8
RC Frame and Infill Confined Masonry
Construction Sequence
First RC frame is made, later the brick infill wall is made.
First the brick wall is made and later the confining RC elements are
added.
Size of Elements The beam and column of the RC frame are relatively larger.
The confined vertical and horizontal members are relatively smaller.
RC Frame and Infill Confined Masonry
Behaviour during Lateral In-place effects
RC Frame is designed to take the vertical as well as lateral loads while the brick infill walls act asstruts.
The brick wall and the confining elements together act as one element to take the vertical and horizontal loads.
9
13
(b) Rocking of Masonry Piers Earthquake response of a hipped roof
masonry building - no vertical reinforcement
is provided in walls.
(a) Building Components
(c) X-Cracking of Masonry Piers
3. Cracking of Masonry piers
Bulging and Splitting of Stone Wall: If there are not enough
through stones to bind two faces of the walls together, the wall
behaves as two separate walls.
15
Schematic diagram of the wall section of a traditional stone house- thick walls without stones that go across split into 2 vertical layers.
5. Out of Plane Failure: As long walls behave differently at
different points along their length during vibrations, long walls are
vulnerable.
16
6. Column damage during earthquakes (Short column effect)
If the infill wall is not of full height of a storey, it adds to the stiffness of
the column over a part of the height of the column. Since stiffness
means resistance to deformation, portion with walls resists the
earthquake forces, while the remaining part of the column is exposed
to larger amount of lateral forces. If such part is not designed to resist
these loads, it can suffer significant damage during an earthquake.
17
19
Overturning
Thick Wall (1½ brick)Versus
Thin Wall (1 brick)
Short Wall (1 brick)Versus
Tall Wall (1 brick)
Overturning
1. A thick wall is more stable than a thin wall.
A wall of short height is more stable than a tall wall.
2. A short wall is more stable than a long wall
Walls longer than 7m length needs to be suported by cross
walls or pillasters.
20
Large portion of
walls not supported
by cross walls
Cross Wall
Inertia force
from roof
Good support
offered by cross walls
Cross Wall
Short wall
Long wall
3. When an earthquake strikes, walls perpendicular to the
direction of the earthquake are subjected to stronger
force. Here, given the direction of the earthquake, walls
in B tends to fail.
21
Toppling
Direction of
earthquake
shaking
By connecting adjacent walls properly, box action ensures that
the entire structure moves together and the loads are transferred
from the weaker walls to the stronger walls with respect to the
direction of the shaking.
22
Toothed joints in
masonry courses or
L-shaped dowel
bars.
Direction of
earthquake
shaking
1. Masonry Bonds: English Bond
Avoid vertical joints by ensuring that proper bond is
maintained.
25
(Baker, Laurie, 1988, Brick Work)
26
1. Masonry Bonds: Flemish Bond
One must avoid vertical joints by ensuring that proper bond is
maintained.
(Baker, Laurie, 1988, Brick Work)
27
1. Masonry Bonds: Rat Trap Bond
One must avoid vertical joints by ensuring that proper bond is
maintained.
(Baker, Laurie, 1988, Brick Work)
28
Importance of Staggering Joints
Joints in a wall should be staggered such
that the wall behaves as one monolithic
unit. Otherwise, during the effects of a
hazard, the wall may behave as
separate parts and split where the joints
are not staggered.
(Baker, Laurie, 1988, Brick Work)
2. Random Rubble Masonry
At regular intervals, the random rubble masonry should be
brought to leveled course.
29
Random Rubble
Masonry must be
done in courses
Max.
Course
height =
600 mm
30
All voids must be filled completely with smaller stones of
different sized stones and minimum possible mortar.
Placing Through Stones in a Stone Wall: Through stones are
used to hold the layers of the wall together to prevent splitting.
31
Provide at least one “through stone”
at every 1200 mm horizontal
distance in the masonry and at
every 600 mm height in staggered
manner.
1. Minimum Distance until a
through stone is required:
At a distance of every
1200 mm for a 400 mm
thick wall and at height of
600 mm.
2. They must be staggered
as much as possible across
the wall.
3. If appropriate through
stone is not available,
concrete block of required
length, may be cast in-situ
to create such stone.
32
Placing Through Stones in a Stone Wall
3. Horizontal bands in a structure are important to ensure that
the entire building behaves as one structure.
33
Bending and pulling in lintel bandsBands must be capable of resisting these.
Difference between a Band and a Beam:
A horizontal band ties together
all walls of a house, and
therefore, helps transfer the
horizontal loads between weak
and strong walls depending on
the direction of the forces.
A beam is meant to take the
vertical load of the roof or other
storeys, which it transfers to the
walls or columns beneath it.
34
Horizontal Forces due to earthquake, wind etc.
Vertical Forces(dead and live loads) in a house
Seismic Band
Structural Beam
35
Requirement of Bands in different Seismic Zones?
1. Bands are Important to Strengthen Masonry Walls
2. All other bands are required in Seismic Zones IV and V.
3. Sill Band can be avoided in Seismic Zones II and III.
4. Details of Sill Band, Lintel Band and Eave Band
These Bands are to be made in the same way as the Plinth Band
(C8). Things to be kept in mind are:
1. In an RC band, the longitudinal bars must be raised from the
brick and 25mm inside from the face of the wall.
2. The junctions and overlaps will have 450 mm of overlap of
the longitudinal bar, which will then be tied together.
3. The ends of the cross ties should be bent inwards across the
band.
4. Bands can also be made with other materials, like bamboo
ladder and timber ladder.
5. The junctions must be secured so that they transfer the loads
evenly.
36
4.1. Connection of Eaves and Gable Band
The junction between the Eaves and Gable Bands must be
secured to ensure box action.
37
Provide two bars of same size in the Eaves Band and bent at the
angle of the gable band. These will be overlapped with the bars
in the Gable Band, which will make a secure junction to ensure
the loads transfer evenly.
38
4.2. Gable Wall and Gable Beam
The height of the gable band should be not more than 1m above
the Eave Band. The Eave Band and the Gable Band must both
be provided.
39
Gable Height
Max. 1m
No Eaves Band Eaves Band provided
If Gable Wall is taller than 1 m, it is better to build it with light
materials, like CGI sheet, wattle & daub or timber planks.
40
Timber or CGI gable walls
Gable Height Max. 1m
4.3. Anchoring of Roof to Walls
Anchor the ridge beam of a sloping roof and the intermediate
beams of the roof to the Gable Band, so that the entire house
behaves like a box.
Step1
Install a 12mm diameter 250 mm long bolt with a 100X100X5 mm
MS plate welded at it’s bottom in the band, where the ridge
beam or rafter sits on the Gable Band.
41
Step 2
When the concrete of the band is poured and becomes hard,
the ridge beam with a through hole can be attached over the
bolt and then anchored down using a washer and a nut.
42
5. Vertical Reinforcement
Vertical reinforcement is important to aid the transfer of stresses
directly to the ground, especially at critical points, like corners
and around openings.
43
(a) At each room corner on
all floors
(b) On either side of door
openings, and preferably at
window openings.
(c) In Cyclone Zone V under the ridge in gable wall
5.1. Vertical Reinforcement in Brick walls
The brick bonds are arranged in such a way that a cavity is
created at the centre of the L or T junction around the
reinforcement bar. The cavity is later filled with micro concrete in
450 mm lifts. The details of brick bonding with cavity for vertical
reinforcement are given in C9. The reinforcement bar must be
anchored at the foundation.
44
5.2. Vertical Reinforcement in Concrete blocks
While using concrete blocks, use solid blocks which have a key hole
or hollow blocks with a slot keep the reinforcement bar in the
centre of the cavity. This cavity can then be filled with micro
concrete.
45
6. How to strengthen slender and long Walls
46
In long walls (more than 7m), buttresses must be provided.
7. Load Bearing Non-Masonry Walls
Earthen walls are just as brittle as other masonry walls, and
need to be protected from moisture in the air.
47
1. They need vertical reinforcement as well as bands to be
strong and hazard resistant.
2. Their behaviour is similar to masonry walls, except when there
is a lot of moisture in the atmosphere. Earthen walls, if not
stabilised, lose strength in such a situation and may fail.
48
7. Load Bearing Non-Masonry Walls
8. Openings in Masonry Walls
The vertical reinforcement bars allow the entire house to act as
one and bend accordingly, rather than shake as separate
elements and cause more damage.
49
Vertical reinforcement bars
cause bending of masonry piers
instead of rocking.
Vertical reinforcement bars in
masonry walls; wall behaviour
is modified.
i) Asymmetric openings cause uneven stresses on wall
and can cause more damage.
50
House with asymmetrically arranged wall
openings can suffer more damage. For
symmetry place identical openings in
opposite walls.
When possible, place
door in the center of
the wall with openings
placed symmetrically
on both sides.
ii) Too many Openings on the same Wall cause Wall
to collapse.
51
Walls with too many door and window
openings close to each other could
collapse easily. Openings should be
restricted to small sizes and few in numbers.
In smaller rooms,
provide no more
than one opening
in each wall.
iii) The Distance between inner edge of the corner and
the edge of the opening must be significant.
52
If the gap “E” between inside
corner and a door or a window
opening in a wall is too small,
the wall can get damaged
easily.
The gap “E” should be
larger for more
strength.
iv) Distance between inner edge of wall and and the edge of the opening should be at least ⅙th of height of wall.
53
A > H/6
H A
v) Avoid too many Openings on the same wall
54
Avoid large central openings or too
many openings in a wall.
Identical window
openings in
opposite walls.
Opening distributed in
more walls.
vi) In a cyclone prone area, ensure that all doors and
windows can be sealed properly.
55
Make all doors and windows such that they can be tightly shut
and sealed during cyclone.
vii) The same lintel level should be maintained for all
openings. Many different levels and sizes of windows
cause stresses to affect the wall in an uneven manner
and lead to more damage.
56
Maintain same lintel level for all openings. Try to keep all windows of same
size. Many different sizes and levels make walls unsafe in earthquakes.
Summary
1. Typical damages to walls during various hazards: Failures of corners,
diagonal cracking around windows, and splitting of thick walls
2. Basic principles of making walls and openings: We discussed box action,
slender vs thick walls, long vs short walls and corner strengthening.
3. Details of makings walls, including vertical reinforcement, different types
of bonds, importance of horizontal bands, importance of staggering the
joints, through stones, confined masonry and buttressing.
4. Windows and doors play a pivotal role in hazard resistance. The size of
the opening, its location with respect to the wall and other openings, all
affect the way the wall will behave during a hazard.
5. Openings should be symmetrically placed. They should not be too close
to each other. There should be enough wall area between two
openings.
58